Photosensitive elements which can be used in image-reproduction processes are well-known in the graphics arts industry. Such elements are usually exposed to actinic radiation through an image-bearing transparency, such as a color separation transparency, to produce an image which is either a positive or a negative with respect to the transparency used. Positive-working elements produce an image which is a duplicate of the transparency through which they are exposed. That is, the colored regions of the transparency are also colored in the imaged element and the uncolored regions in the transparency are uncolored in the imaged element. Negative-working elements produce an image that is the reverse of the transparency through which they are exposed. That is, the colored regions of the transparency are uncolored in the imaged element and the uncolored regions in the transparency are colored in the imaged element. Ordinarily, a positive-working element is exposed through a positive transparency to produce a positive image, and a negative-working element is exposed using a negative transparency to produce a positive image. After imagewise exposure, the photosensitive elements may be developed by washout of soluble image areas, by peeling apart, by toning with a colorant, or combinations of these techniques.
Such photosensitive elements are widely used in pre-press or off-press color proofing systems to simulate the images reproduced by printing. Pre-press color proofs include overlay systems and surprint, or single sheet, systems. In an overlay proof, each color is on a separate transparent sheet. The individual films are assembled in register and viewed as a composite against an appropriate background, e.g., an opaque reflective white sheet. In an overlay system the individual colored elements remain separable and can be combined or viewed separately.
Conventional overlay proofing films are precolored by their manufacturers. Thus, in the preparation of overlay images, the operator is limited to those colors provided by the manufacturer. Because of the cost of manufacture, inventory, and distribution, necessarily only a limited range of colors will be available. A number of commercial overlay proofing systems are described in detail in Principles of Color Proofing, by Michael H. Bruno, GAMA Communications, Salem, NH, 1986, Chapter V, "Off-Press Color Proofing Systems--Overlay", pp 133-146, the teachings of which are incorporated by reference.
The process of the invention permits preparation of overlay images with specialty, i.e., non-standard, colors from a non-colored, tonable element. The operator can use precolored overlay films to prepare images requiring standard colors and use the non-colored, tonable element to prepare toned images requiring specialty colors. These precolored and toned images can then be combined to form a multilayer, multicolor overlay proof consisting of toned and precolored images. Because the operator can mix the toners supplied by the manufacturer as desired, toned images with an almost unlimited variety of colors can be prepared. Instead of providing many specialty films, the manufacturer only has to supply precolored films in a limited number of standard colors in addition to a single non-colored, tonable element.
There is a need for such a process by which both precolored and toned overlay images can be prepared from a single set of separation transparencies and combined to form a single, multilayer, multicolor overlay proof.
For such a process to be practical, both the precolored films and the non-colored, tonable element must work in the same sense, i.e., both must be either positive or negative working. For example, if the precolored film were negative working and the non-colored, tonable element were positive working, it would be necessary to provide negative separation transparencies to prepare the precolored overlay images and positive separation transparencies to prepare the toned overlay images.
It is also essential that the toned image have the correct left to right orientation when viewed with the toned image down, i.e., away from the observer, and the support up, i.e., facing the observer. This orientation is required to protect the image during normal storage, handling, and use. Therefore, the process must produce a toned image which has the correct left to right orientation when viewed with the toned image down.
Further, such a process must produce both precolored and toned images which have the same right to left orientation as the image being reproduced. None of the images can be a mirror image of the original image.